Negative-working dry peel apart photopolymerizable elements are known. These elements are described as being particularly useful as photoresists for preparing printed circuits including photoresists for tenting. Such elements can also be used in the preparation of both negative and positive images of good quality from one simple operation at room temperature.
U.S. Pat. No. 3,770,438 discloses a dry-developing photopolymerizable layer on a polymer film support operating according to the principle of the polymerizable monomer being present in the layer in a quantity in excess of the absorptive capacity of the binder so that a thin layer of substantially free monomer is present on the surface of the photopolymerizable layer. This free monomer is detectible on the surface of a substrate such as copper as an oily residue when the layer is peeled off of the copper prior to any photoexposure of the layer. The free monomer polymerizes when photoexposed to actinic radiation, to adhere the exposed area of the layer to the copper substrate more strongly than to the film support. The greater affinity of the monomer for the film support than the copper substrate in the unexposed area of the layer enables the unexposed area of the layer to remain adhered to the film support. Different ways for achieving an excess of monomer are used in the patent, e.g., using a hydrocarbon polymer binder and a very large proportion of monomer (77.5% in Ex. 3), using a chlorocarbon polymer binder having a lesser absorptive capacity for the monomer, thereby reducing the monomer content to 40-50% (Ex. 9, 13, 15 & 16), or using a combination of a chlorocarbon polymer (M. wt. about 20,000) and higher molecular weight (about 60,000) poly(methylmethacrylate) to decrease the flow of the layer. The amount of chlorocarbon polymer used ranged from 24.6 to 41.1 by wt., the amount of hydrocarbon polymer from 3 to 29.4% by wt. and the amount of monomer ranged from 24.2 to 65.6% by wt. (Ex. 1, 2, 5-8, 12, 14, and 16). The disadvantage of the dry-developing photopolymerizable layer of this patent was that either the flow of the layer at ordinary room temperature was too great or the fidelity of the image reproduced by the layer was less than desired. As the flow of the photopolymerizable layer was reduced in an attempt to provide a layer that could be supplied in the form of a roll, as required for commercial acceptance, the layer would either not fail cohesively at the boundary between the unexposed area and exposed area of the layer with a smooth, sharp break to give the image fidelity desired or would not fail cohesively at all, i.e., even the unexposed area of the layer would adhere to the substrate when the film support was peeled away. Layers that gave good image fidelity upon dry development were tacky so that it was difficult to remove a cover sheet that may be laminated to a surface of the layer.
U.S. Pat. No. 4,058,443 disclosing another peel apart system states that the mechanical strength of photopolymerizable layers used for dry development are apt to have insufficient mechanical strength which is important when the layer is used as a tenting resist. U.S. Pat. No. 4,058,443 purports to solve this problem by having the binder of the photopolymerizable layer, in addition to chlorinated polyolefin, consist of 10 to 90% of a straight-chained polymeric material having sufficient compatibility with the other components of the layer and having a molecular weight of at least 10,000, with a range of up to 2,000,000 being disclosed. The chlorinated polyolefin is also claimed to have a polymerization degree of 600 to 20,000 which for chlorinated polypropylene (64% by wt. Cl) corresponds to a molecular weight of about 34,000 to 2,200,000. The resist utility disclosed in this patent is as an etching resist. The layers of this patent are either too flowable or when not too flowable, they have deficient image fidelity upon dry development. In addition, the conditions for peeling away the support film to achieve dry development are too exacting for commercial practice. As such these layers have nothing more than laboratory application.
Cohen and Gervay U.S. application Ser. No. 015,245, filed Feb. 26, 1979 discloses dry-developing photosensitive dry film resists containing polymerizable monomer in excess of the absorptive capacity of the layer, photoinitiator system and a plurality of polymeric binders, at least one of the polymeric binders being incompatible so as to be present as a dispersed phase in the photopolymerizable layer to reduce the cohesive strength of the layer. The incompatible polymeric binder in the photosensitive layer has a glass transition temperature (Tg) of less than 70.degree. C. It is desirable to prepare other photosensitive elements possessing the advantages of U.S. application Ser. No. 015,245 which contain incompatible polymeric binders having glass transition temperatues above 70.degree. C. which are not only useful as photoresists but for other uses including the preparation of high resolution negative and positive color projection transparencies, etc.